Wrought products and methods of making same



Oct. 16. 1956 P. E. CAVANAGH 2,767,087

WROUGHT PRODUCTS AND METHODS OF MAKING SAME Filed Dec. 14, 1953 3 Sheets-Sheet l CRUSHER SCREENSOR OXIDE AND OR SIZING GRINDER- DEV/CE.

ADMIXTURE CONCENTRATOR CANGUE NON- OXlDlZ/NG ATMOSPHERE a HOT HOT SHA PING SUPPORT WORKING -WORKED APPARATUS PRODUfl'T REDUCING AND SINTER/NG CHAMBER PATRICK E". CAVANACH.

b Wg

Oct. 16, 1956 P. E. CAVANAGH 2,757,087

WROUGHT PRODUCTS AND METHODS 0F MAKING SAME Filed Dec. 14, 1955 s She ets-Sheet 2 DIFFERENTIAL J DEFORMAT/ON I'ZYF,JDIFFERENTIAL W I II I DEFORMA 27 4mm PATRICK [.CAVANACHZ WWM Oct. 16, 1956 P. E. CAVANAGH 2,767,037

WROUGHT PRODUCTS AND METHODS OF MAKING SAME Filed Dec. 14 1953 3 Sheets-Sheet 5 y v IIIIIIIIIIIIIIIIIIII/ I PATRICK E. CAVANACH w wwfgi United States Patent I O 2,767,118? WROUGHT PRODUCTS AND METHODS or MAKING SAME V Patrick Edgar Cavanaglf, (lakville, Ontario, Canada Original application December 23, 1952, Serial No. 327,575. Divided andsthis application December 14', 1958, Serial No. 398,169

5 Claims. (CI. 75l211).

This invention'relates to themanufacture of metal products and particularly to methods adaptable to large scale operations for forming wrought ferrous metal products; for example, sheets, plates, strips, bars, rods and the like, directly from compositions that comprise previously unreduced oxygen bearing metal compoundso'r from bodies below theoretical full density of the metal thereof, hereinafter defined as subdensity metal bodies.

This application is a continuation-in-part of my co pending applications SerialNo's. 155,278, filed April 11, 1950, now abandoned;-231,074, filed June 12, 1951, now abandoned; 232,921, file'd' June 22, 1951, now abandoned, and a divisional application. of 327,575,- filed December 23, 1952, now Patent Number' 2,686,118, issued August 10, 1954.

By a subdensity metal body, I mean a metal body having a density which is substantially less than the density of the solid material thereof, by reason of voids in -the body. It will be understood that such metal body may be formed of a singlemetallic element'or ofan' alloy or mix ture of a number of metals with or' without other materials. ln-an important specific sense, the'present invention is concerned with ferrous metal bodies, whereinthe predominant component is iron', examples being comp'os'i tions corresponding to various steels, other ferrous alloys and the like; I

While the invention relates'to the formin'giof wrought ferrous metal products from" subdensity bodies, it'is" preferred to practice the inventionupomthat classof s'ub' density body which is formed from controlled density metals including techniques associated with manufacture of the latter as set forth in the-said co-pending applications. A controlleddensity metal body may be described as a body produced by complete or partial reduction of oxygen bearing material at temperatures below the melting point of the body, in suitable apparatus whereby the body is produced and proportioned to a predetermined shape of predetermineddimensions'j during: the reducing process; said oxygen bearing material comprising a compound or compounds of one or more metals which, before reduction, may or may not have been mixed with other metallic and/ or non-metallic materials; said body having predetermined surface conditions 'and a pr'edetermined density between 5 percent and 100 percent of the theoretical full density of the solidmat'erials of said body.

Prior proposals for forming ferrous products directly from oxides or from subdensity. iron particles have involved a complex series ofope'rationsand have often been directed to the formation, at the outset, of a large ingot or billet of high density. The ingot or billet is sometimes required to be so compactedin formation as to reach the equivalent of full, solid metal density, or is produced in some otherspe'cial'form' of lamination or the like, as heretofore believed necessary for passageof the billet through the rolls ofa conventional rolling-mill-.-

In contrast to prior methods, ;the present invention differs largely inconcept in having for a main object, the provision of a direct method adaptable to large scale a 7. ce.

manufacture for forming hot worked metal products of maximum density, e'. g., substantially solid metal density, while eliminating the necessity of forming an ingot of high density or of performing other costly intermediate steps, and wherein the product to be produced may correspond, for example, to the product ordinarily obtained from the final rolls of a rolling'mill adapted to work upon an ingot.

Another object of the invention is to provide a method of makingsheet steel andsimilar products of a chosen predetermined thickness directly from a subdensity metal shape proportioned to be reduced to said predetermined thickness when worked by passage through rolls to the point of maximum density. By the term maximum density I mean the maximum density attainable in practice by the body.

I have discovered that a subdensity mass of metal may be successfully reduced to maximum or full density of the metal itself while substantially unconfined by an enclosing die, mold, or the like, by following techniques in accordance with the invention. In the hot working of subdensity ferrous metals, one criterion according to the inventionrequires that the hot working be limited to that sufficient'to develop lessthan a permissible amount of differential deformation. By the phrase differential deformation, 1 mean the difference in elongation in any direction of the core port-ion of a subdensity metal body compared to the elongation of the surface portions thereof during working;- A second criterion requires that if a productis to bewrought so as to have a substantially uniform density throughout, the working, e. g., hot working, should be accomplished by carrying the deformation in one operation (by the application of a continuous force, as in a'single rolling pass) from a point Where the body haszero diiferential deformation or less than the differential' deformation permissible under the first criterion above, to a point where the density of the body has suffi ciently approached maximum density as again to reach a condition of less thana permissible differential deformation; A third cn'terionrequires that the subdensity metal article be proportioned having regardto the nature of the product to be made.-

A- still further object-of the invention is to provide a; process for forming hot'worked ferrous products wherein the grain size of the re'sultingferrous product is substan tially determined by the grain size of the particles of iron oxide fromwhich the ferrous product is formed, whereby properties normally attributed only to extensively worked ferrous'products can'be attained with a small amount ofwo'rking.

Other objects of the invention will be appreciated by a study of the following specification, taken in conjunction with the accompanyingdrawings.

In the drawings:

Figure 1 is a' flow sheet layout of a preferred process according to the invention;

Figures 2A to 2D illustrate the manner of hotworking a= subdensity frr'ous' article according to the invention;

Figures 3A'to 3D illustrate the manner of hot workinga-modified' form of slab according to the invention to obtain'a'clean edge condition on a strip, bar or sheet product;

Figures 4A to 4B illustrate methods of hot working a subdensity ferrous article according to the invention;

Figure 5 isa sectional view of apparatus for forming a shaped cohered' subdensity article; and

Figure 6 is a diagrammatic perspective of the formais crushed and/or ground, as may be required, and sized by suitable screens or other sizing device to obtain a preferred particle size distribution and bulk density in the oxide to be used in the present process in accordance with the requirements of shrinking and swelling characteristics of the oxide during reduction, grain size in the final product, rate of reduction or permeability of the oxide mass to the passage of reducing gases, and the desired density and strength of the subdensity metal shaped article produced for the hot working techniques disclosed herein. Silica and other gangue constituents may be removed from the chosen form of iron oxide material preferably by dry concentration, for example, by suitable concentrator such as a magnetic concentrator of the class disclosed in Swedish Patent No. 120,710 granted November 27, 1947, to E. H. H. Eketorp, et a1.

Following concentration, the sized and concentrated oxide may have admixed therewith, finely divided alloying constituents or foreign bodies in accordance with the requirements of the product to be produced.

The sized and concentrated oxide, with or without admixture, is loaded into a shaping support in the direct forming apparatus, which support is of a nature defining the shape of the subdensity article produced therein during the reduction process. The present process does not rely at this stage upon the application of positive pressure techniques such as extrusion or compaction of the ore by large pressures. The oxide may be freely loaded into the shaping support, this particular technique permitting the present process to be operative with an extremely wide range of ferrous oxide materials which otherwise would react unfavourably if unduly compacted, due to shrinkage or swelling characteristics.

While in the shaping support, the oxide is heated and subjected to a reducing gas in the reducing chamber as indicated and the reduced oxide particles are heated to a suflicient temperature to form a cohered subdensity article of sufi'icient structural unity permitting removal from the shaping support and of suflicient strength to be handled as a non-friable cohered body of predetermined dimensional characteristics adapted to be hot worked in the hot working apparatus. It is contemplated that the strong coherence of the shaped body be achieved by heating it to unite its metallic composition, e. g., at least to a temperature for sintering its particles or portions strongly together. It will be understood that in practice, the reduc 'ing and cohering operations may be at least in part simultaneously effected; for example, the last stages of a desired extent of reduction may be performed while heating is being continued at a temperature for efiectuating or completing the described coherence.

The hot working techniques of this invention may be discussed with reference to Figures 2 to 4. The subdensity ferrous metal shape at Figure 2A may be hot worked to compact the surfaces thereof to maximum density as indicated by the maximum density outer layer 11 at B surrounding the lower density core 12. I have found that it is permissible to so compact the outer regions of such body within the limits of an elongation giving rise to stresses between the outer dense skin and the inner low density core of a limited value. If the structure shown at B in Figure 2 is reduced in diameter by further hot working to a point where the skin 13 is of substantial thickness as compared with the diameter of the core 14 as at C, then the elongation of the skin 13, if in excess of about 10 percent, may give rise to undue stresses, causing failure imperfections 15 in the skin. It is for this reason that the ordinary swaging machine or rolling mill practice is not operative to form a maximum density rod from a low density subdensity structure unless methods are modified to follow the methods of the present invention.

I have found that a section of entire maximum density as at 16 in Figure 2D having substantially no voids, as would be the case of an ordinary steel rod or the like, may

be formed by working the subdensity article shown at 2A to maximum density under the action of a continuously applied force, that is, in one operation through a swaging device.

In forming strip or sheet of maximum density, the subdensity metal slab must be of predetermined shape and dimensions to attain the desired results. For example, a subdensity ferrous article 17 shown in Figure 3A may be reduced in one hot pass through the rolls to form the maximum density product 18 of Figure 3B. If the article 17 is of insufficient aspect ratio, i. e., the ratio of width to thickness is too small, the product 18 may have edge faults 19. In many cases, small edge faults may be eliminated by edge trimming of the resulting sheet. In general, however, edge faults arising from the proportioning of the subdensity slab may be avoided as indicated in Figure 3C by sizing the slab such as slab 20 to a width greater than ten times the thickness. As indicated in Figure 3D, a maximum density product 21 of more regular edge form will result. A subdensity metal slab aspect ratio of greater than fifteen is preferred as giving satisfactory results in most instances regardless of the particular density of the slab which is to be worked to maximum density.

Edge fault problems derived from slab proportions will not ordinarily arise in the practice of the invention to form a wide sheet of desired thickness at the point of maximum density of the slab. Accordingly, the proportions of the slab will primarily be determined by other considerations. I have ascertained that slab proportions for purposes of the invention are derived from a consideration of relative volumes according to the relation Vs D max Vmin Ds Where Vs is the volume of the subdensity slab;

Ds is the density of the subdensity slab;

V min is the volume of the maximum density product,

as it comes from the rolls;

D max is the density of the maximum density product.

D max-V min =20 cubic units The elongation in the direction of rolling will be say 30 percent. The elongation in the lateral direction will be say 10 percent.

The length of the slab may then be The width of the slab may be The thickness of the slab may be Vs 2O =0.57 units Slab dimensions 7.7 X 4.54 x 0.57

Although the aspect ratio of such a slab is less than the preferred minimum, there is a possibility of obtainmg satisfactory edge conditions assuming regular slab r ed es, good o li pra i e and heusiial amounto edg finishing or trimming in the final product.

While proportioning techniques set forth herein apply largely to methods, of forminga product of maximum density material in its entirety, the same techniques generally apply to portions of a slab which may be reduced to maximum density while the remainder is substantially unworked. For the purpose of calculation of general slab proportions, the unworked portion maybe assumed to retain its original density. I

Special techniques also arise in the control over other faults which may .occur in the formation .of strip, bar or sheet, Forexample, in Figures 4A to 4D, the longitudir al section of ferrous metal bodies is illustrated. In Figure 4A, a suhdensity ferrous metal article 22 is shown of a specific length y. As in the technique discussed Withreferejnce to Figure 2, the ,subdensity article 22 may be rolled or otherwise compacted to form skins of maxi mum density 23 and 24 on either side of a low density core, 215 such as by a single pass through the rolls while the. article is hot, wherein a differential deformation in the case of ferrous products will be of the order of about 5 percent. As indicated, the skin portions may undergo an elongation of about per cent or less during a rolling operation; however, as shown in Figure 4C, if the structure of 4B is subjected to further passes through the rolls, unduedifferential deformationmay occur and the skin portions may elongate to an extent setting up stresses during rolling in excess of the strength of the skins. Thus one may obtain a core 26 of low density having thereover the skins 27 and 28 having faults 29 and"30. After one pass through the rolls to form a product such as in Figure 4B, one risks the condition of Figure 4C upon attempting to roll further to maximum density.

It will thus be evident that elongations between about 1.0 percent and about percent represent a substantially difficult range to be avoided in the working of subdensity ferrous materials in particular. While I believe that differential deformation should not exceed about 5 percent for many ferrous metal products, this will not be found inconsistent by skilled persons employing these general limits in conjunction with factors of safety assuring desirable results in any circumstance. The degree of perfection required will be dictated by specifications for the product.

If a product of maximum density throughout is required, I subject a subdensity metal article such as the article 22 of Figure 4A, to a continuously applied force such as by a single pass through the rolls, hile hot, to

reduce it to maximum density, at which an elongationof about 30% or more will be experienced, as indicated in the case of the product 31 of Figure 4D. As before mentioned, in a more general sense an important criterion of working requires that if a product is to be wrought so as to have a substantially uniform density throughout, the working, e. g., hot working, Should be accomplished by carryingthe deformation in one operation (by the application of a continuous force, as in a single rolling pass) from a point where the body has zero differential deformation or less than the dilferenti'al deformation permissible under the first criterion above, to a point where the density of the body has sufliciently approached maximum density as again to reach a condition of less than a permissible differential deformation. It will therefore be understood that the single application of continuous force is exerted to carry the body to a relatively high prefer bly uniform density and to not more than a predetermined differential deformation. In the formation of a sheet, strip or bar, this technique must be taken into account, along with the technique disclosed in the diss ion o u e I have successfully formed products according to the invention by employing a reheating technique wherein the subdensity ferrous article is allowed to cool and is then reheated in a reducing or non-oxidizing atmosphere before Working. 7

Thus Tables I to IV listinformation pertinent to ex: amples of practice of the invention applied to three different iron oxide materials.

TABLE I Mill scale 73.6%.

200 lbs/ta? or 3.2.gms./cc.

Reduction temperature Holding time (reducing and coheriug time in 20.

hours). Slab density '3.0gn 1s./ce. Slab thickness- 0.515 inch. Single hot pass reduction 75.7 percent. Sheet thickness .i 0.125 inch. 7 Sheet density 7.5 gms./cc. (computed).

Cold rolling reduction. 70 percent.

Cold rolled sheet thickness 0. 8 1110 Annealing temperature 1400 F. Annealing time 30 m n.

TABLE II Old bed concentrate Total Fe 70.2%. Bulk density .,3.5=gms./cc.

Sieve analysis Reduction temperature 19 80 i Holding time (reducing and cohering time in 12%.

2.1 gms./ cc.

'gAlO inch.

Single hot pass on heet thickness 0.085 inch. Sheet density 7.7 gmsJcc. (computed); Gold rolling reduction. 40%. Cold rolled sheet thickness 0.046 inch. Annealing temperature 1l50 F. Annealing time 30 min.

TABLE III Mag iron concentrate 14.0 gms 99. 5 g ns.

Reduction temperature 1980 F. Holding time (reducing and cohering time in 10.

'hours). Slab density 2.1.grns./cc. Slab thiclmess"- 0.410 inch. Single hot pass re uc 80.7%. Sheet thickness.v 0.079 inch Sheet density... 7.7 gms /cc (computed). Cold rolling reduction 6%. Cold rolling sheet, .thickne 0.040inch. Annealing temperature 1150 F. Annealing time 30 min.

TABLE IV Properties of rolled sheet (test data) Mill Scale Old Bed Mag Iron Hot Rolled:

Rockwell B 60 70 67.

Hardness.

Bend Tests 180 on VL-.. 180 on V 210 on Ult. Tensile 52,000 p. s. i 54.300 p. s. i.-. 59,000 p. s. i.

Elongation 19% 12% 16%.

(tested). Grain Size 7-8 7-8 7-8. Cold Rolled:

Rockwell B 103 98 99.

Hardness.

Bend Tests 45 45 50.

Ult. Tensile 102,000 p. s. i 96,200 1). s. i. 99,000 p. S. i.

Elongation 1% 2% 1%.

(tested) Annealed:

Rockwell B 60.5 55 50.

Hardness.

Bend Tests.- bent on self. bent on self. bent on self.

surf. opentears tears ings. through through.

Ult. Tensile .L 49,000 46,300 47,000

Erickson Ductll- 4.8

ity Test.

In the foregoing examples, it was proposed to form a 3 inch wide strip of hot rolled steel about 12 inches long and less than inch thick. Accordingly, a subdensity metal slab was made from each of the three iron oxide materials noted, 3 inches wide and 12 inches long and of a low density of about 2 to 3 gms./cc. since such low density would otter a low resistance to the passage of reducing gases. Assuming a slab density of 3 and having regard to volume-density relations as set forth herein, the slab thickness required to produce a inch sheet was about V2 inch, giving a very low aspect ratio for the slab of 6 to 1.

The mill scale selected was obtained from a continuous hot strip mill and accordingly was relatively low in residual alloys and carbon content. Upon analysis, the mill scale showed 73.6% iron and 0.48% silica.

Since it was desired in all of the above examples to predetermine the grain size of the resulting rolled product to a conventional magnitude, a substantially corresponding sizing of the mill scale was carried out by grinding in a ball mill to minus 60 mesh screen size. The ground mill scale was screened to provide the particle size distribution shown in Table I of relatively low bulk density consistent with the delivery of a relatively low density metal slab and accordingly conducive to rapid reduction. The bulk density of the ground and sized mill scale was determined by pouring it into a graduated flask vibrated for thirty seconds to constant volume after which the volume and weight of the contents were measured and the density calculated.

Permeable molds were then made by mixing 3% of a thermo-setting plastic binder with foundry sand as in we'll-known shell molding techniques. A shell mold was formed with this mixture over a metal pattern heated to 500 -F. The finished mold was removed from the pattern and .after cooling, was loaded with the prepared mill scale. The loosely filled mold was then vibrated to settle the loose oxide as much as possible and a shell mold material cover was placed over the upper end of the loaded mold.

A convenient way of performing the formation of the subdensity article within this mold is illustrated in Figure 5. A plurality of loaded permeable molds 32, having covers 3211 were placed, one above the other, in a cylindrical container 38. A metal sagger of 15 inches inside diameter and 18 inches in height, was used. The saggers were fabricated from sheet alloy steel (15 percent chrome, 35 percent nickel). The bottoms 34 of the saggers were formed of cast a'lloy, each of the saggers being coated with a suitable high temperature enamel 3'5 to reduce oxidative tendencies. In loading the molds into the saggers, a reducing mixture 36 was first placed on the bottom of the saggers and then the molds .32 were placed theneabove spaced each from the next by a layer 37.01: the reducing mixture with a final layer 38 of the reducing mixture to a level within 2 inches of the top of the sagger. A one inch layer 39 of loose iron ore of finely divided form was placed over the topmost layer of reducing mixture to form a seal over the open end 40 of the saggers and to prevent reoxidation of any iron produced in the sagger.

The reducing mixture 36 was thus placed entirely outside the material loaded into the molds and comprised a mixture of coke breeze and limestone wherein the coke breeze was of at least 80% carbon, completely dry and sized to minus 8 mesh screen size; 15% by weight of minus 4 inch limestone was added to the coke breeze to act as a desulphurizer to take up the sulphur from the coke and prevent it from going into the iron particles as they were formed from the oxides being reduced in the sagger. The ratio of coke to oxide in the saggers was of the order of 10 of coke to 1 of oxide by weight.

The loaded saggers were heated to a reducing tcmperature by passing them through a tunnel kiln at suflicient speed so that the time at a temperature of 1980 'F was 20 hours. This period of time enabled the reduced oxide particles to cohere together to form a non-friable cohered mass which was allowed to cool over a period of twentyeight hours to 200 F. The time at temperature during the reducing and cohering period was of a time period which, in conjunction with the average size of the oxide, the particle size distribution thereof, the temperature and the amount of carbon available from the reducing gas :a temperature between '1900 F. and 2200 at the rate of about 100 F. per hour and which will hold the saggers at this temperature for a considerable period of time, would be suitable for processing of the type indicated.

- In accordance with the invention and as indicated in Figure 6, a subdensity slab 41 of controlled density, predetermined shape and dimensions, is removed from a mold 32 after formation therein by the reducing and cohering process and while heated to a working temperature, may be wrought as at 42 to a uniform density of substantially a maximum value by applying a continuous force such as by the rolls 43 set substantially to the thickness of the product desired.

In the present example, subdensity metal slabs con forming to the shape of the molds were removed from the saggers after cooling and were reheated in an atmosphere of nitrogen containing about 30% hydrogen in an electric furnace to a temperature of 2100 F. and held for ten minutes.

The rolls of a small mill were set to produce a sheet in one pass of the slab to a thickness of 0.125 inch. After passing the heating slabs through the rolls so adjusted, a reduction of 75.7% was eifected in one pass delivering a'density in the final product of 7.5% being substantially the point of maximum density of the material being Procedure fq h ed th has iron and 91st as he am h m scale Th cre n d hhutihn d bulk e s y and a alysis f he r s ow in the. tables. In both cases, the ore was magnet cally cone centrated after grinding to remove mostof tghe' gang u e. 5

The slab sizes were the same and {the qoke tie-ore ratio the same as for mill scale. The holding "(tempera ture was ou or masher; and 2. hou s .1 9 t 1 b d- As a resu th dou h oi the labs Prod ced was ll in both cases and the carbon content was 0.27% e he mag n lab nd 8 o the Old be ab- The s ab h chness szw 0,410 .ih91 1 ft r rqllihg, reducti n o abou .0% in a sin e Pas a ter r hea in o Z1Q n h d o en Plus nit o hje here, the. resuhi s sl bs had a comp te dens y o 7 ma ily; ue to th lo a e at o o t e labs h fiqr to he, ed e fa i n t e fin p odu ts ecurre .As; d c t d n e foregoi g ta s, l o he sh t ht ed by o o ng in du pas to sle s y, wer he su je ted we c ld ollin r duction an lQhlQd- Me a al t st were, ard d out for a h o the hot rolled, cold rolled and (annealed products as] utlined in Ta e b er e thath r i size th hot rolled products was between 7 and 8 after one, hot Pass. A e e u er o ra n s z to h t rolled steels range between about 4 and 8, after a large number of hot passes. Th e n m rs r ra n si e are na qordance with the classification of the American S0- ciety for Testing Materials, denoting the number of grains pe q a i a 0 ma ifi t on: i no w hy that a comparable grain size to that aceomplished in r n ry t e was a ed y the Prese t imwes y a control exercised on the sizing of the ore. The struc% tural properties listed in Table IV illustrate the accent.- plishment of desirable structural characteristics by one not p s o e hdw y meta s uh me tlh u the rollsto maximum density and also show satisfactory properties after col-d rollingand annealing,

The subdensity articles formed, for. the. purposes of fio'rming the maximum density sections, need not be of a high density themselves. This invention specifically. contemplates the advantage to be gained by making these subdensity articles of a low density (i. e., less than half the value of maximum density, 'i n'v somecases aslow as one-fi th; u sufiihient ho cc mp i a cohered body) s that the oxide mass may offer relatively low resistance to the passage of reducing gases therethroug h thus permitting very reduction ei-mes. Space is prov i voids of the mass to accept swelling acteristics of the oxide particles during redu characteristics are discussed in some detail in a paper by the present inventor entitled Pelletizing of Iron Bearing Fines by Extrusion and reported in 1950 Proceedings, volume 9, page 54, of The Amerieanlnstitute of Mining and Metallurgical Engineers.

While [the space provided by the voids generally assists in controlling shrinking and swelling characteristics, it is particularly contemplated according to the present invention, to mix shrinking :and swelling ores mo cancel out such characteristics to a degree permitting a closer dimensional control than has heretofore been possible with most iron ores. The problems are not critical in the preferred practice of my invention wherein the shape of the su-bdensity article is determined during the reducing process. However, Where subdensity metal shapes are 6 formed directly from the oxide by prior methods, the prop-ortioning of the shapes taught herein iior working purposes may not be realized or such prior methods may not be operative with many ores unless a blend of 'a plurality of ores of ditierent dimensional change during reduction is used in accordance with the present invention.

While certain limits of differential deformation have been discussed herein, it must be appreciated that the permissible dilierential of deformation between the core and skin portion depends upon the material of the subdfi y and th hat wh s ts i raihre, a

e" hatur 'hi t e o wet a e achie d unde speci 9.n-

. tha n l n a ubd u i s ab o o a p o uct ha in solid metal den it the. slab be hot rolled with sufficient. reduction and elongation in a single pass to carry {he body directly from its unworlced subfiflwity state to sub; stantially density. It will be understood, however, that a rolling pass which in the above general a hi n ches s a s bst a and te e hl t e mhi Pa t of the defior-mation necessary to reach maximum density may sometimes be safely accomplished (in the course of s shin mazdmum dehsity) by p e m o u quent passes or both; e, g., hot rolling passes preferably representing only 'a minorpart of the total density change in reaching the solid-metal (or otherwise substantially unifi rm) den y s at I For instance, in some cases it has been found possible to carry a subdensi-ty slab of ferrous metal, having a. density of about 2 to 3 gms./cc., to a density of about 6 gms/cc. in a single, major, hot rolling pass, Without impairing the structural integrity of the body. W In such operation, the Working is found to. be carried (in the sin sh? Pas yond the range sl hs o e n he d fiersntis de orm ih is e ce s v h dy being this. brgught, to a point where the differential deformation is again safely small and Where .a substantial density inrease ha resum b cur ed throughout e y- Thickness reduction to maximum density, say about 715 gms./ cc. can then be completed with one or more further passes; e. g., hot rolling passes. It also appears possible in some cases to employ a preliminary hot pass or passes on the unworked subdensity slab before proceeding toreduce it throughout to substantially uniform, high density s xplained n e fo e oin o else e h rein, t uc prelim na y pe a o (w c i pr id d e hins 611 a o density cor sho d P f ably k e below the limit of permissible differential deformation (i e mit explained hi om d an w h i ure 31: 241

1 1 ad an a eo sly we c w u h l mi In Q her W rds each r in P s rth n l ontinuous application of deforming force on a body eon- Stituted ho ly o Par l o s d i y ta should pr f-- ah y he s ht s sd 9 dss h d to a i lea n h body in a state illustrated in Figure 4C. Specifically, each single pass (depending on its purpose or its position in a sequence of passes) should preferably be such as either (a) to avoid carrying the first stage of thickness reduction beyond the point of permissible differential deformation (Figure 4B) or (b) to carry the thickness reduction to a much further point, apparently represented by attainment of increased density throughout the body where there is likewise no excessive differential deformation. In a more general sense, an important feature of the invention is the thus exemplified concept that in rolling a subdensity metal body, the characteristics of the rolling pass or passes should be coordinated with the shape, size and density of the body to avoid excess differential deformation, such coordination being achieved by proper control of one or more of the stated characteristics or factors, indeed in effect of all of them.

Methods of the invention are adapted to the formation of a wide variety of products different in structural character and composition from products obtainable from conventional metal forming arts. The subdensity article formed according to the methods set forth herein may be of varied composition and/or density before being wrought. The' composition is determined by the materials loaded into the shaping support for reduction to form the subdensity metal body. Such materials are loaded into the shaping support in zones or layers according to the composition desired in corresponding zones or layers in the final product. The density of such layers is individually controlled generally by sizing of the material therefor. The resulting subdensity body of varied metallic composition is wrought in the manner set forth herein to provide what may be termed a sandwich structure such as a low carbon steel or other ferrous metal subdensity core having integrally joined thereto, thin or thick skins or surface portions of maximum density stainless steel or other ferrous metal composition. The resulting subdensity body may also be wrought to uniform or entire maximum density to provide, for example, a stainless steel sheet having a mild steel core inherently bonded thereto by reason of formation therewith during the reducing process. A wide variety of compositions and densities is thus afforded in metal products of the invention. In all such products, the metals are contemporaneously formed in, and/or derived from, the same reducing and working processes.

In the rolling reduction of subdensity structures, a faulty or inoperative range may be experienced which can be overcome by working through the difi'icult range with a continuous force. The explanation of the difficult range of working by reference to a proposed theory of excessive differential deformation appears to satisfy the results of many experiments. While a differential deformation theory of explanation may be helpful to an understanding of practice of the invention, I do not wish to exclude some other explanation for the phenomena encountered in the working of subdensity bodies. Accordingly, regardless ofhow these phenomena may be explained, I overcome undesirable conditions by working with a continuous force through and thus traverse the difiicult range of rolling reduction.

What I claim as my invention is: 1. The method of forming a metal product comprising commencing with a subdensity cohered metal body proportioned to a finite shape and adapted to conform to the dimensions of said product upon workingsaid body to an elongation in any direction no greater than that required to compact said body to maximum density; heating said body to a temperature insufficient to melt said body but sufficient to avoid structural impairments thereof during working; and finally working said subdensity body to a maximum density by the application of a continuous working force applied substantially throughout the operation of working to maximum density.

2. The method of forming a metal product which comprises commencing with a subdensity cohered metal body proportioned to a finite shape in which the width thereof is' greater than ten times the thickness, heating said body to' a temperature insuflicient to melt said body but sufficie'nt to avoid structural impairment thereof during working, and finally working said subdensity body to maximum density 'by the application of a continuous working force applied substantially throughout the operation of working to maximum density.

3. The method of forming a metal product which comprises commencing with a subdensity cohered metal body having an average grain size of less than one-fiftieth of an inch proportioned to a finite shape and adapted to conform to the dimensions of said product upon working said body to an elongation in any direction no greater than that required to compact said body to maximum density, heating said body to a temperature insufficient to melt said body but sufficient to avoid structural impairments thereof during working, and finally working said subdensity body 'to a maximum density by the application of a continuous working force applied substantially throughout the operation of working to maximum density, said product so formed having the grains thereof cohered substantially to the extent found in a similar metal product made from molten metal casting and working processes.

4. The method of forming a metal product which comprises commencing with a subdensity cohered metal body having an average grain size of less than one-fiftieth of an inch and in which the width thereof is greater than ten times the thickness, heating said body to a temperature insufiicient to melt said body but sufiicient to avoid structural impairment thereof during working, and finally working said subdensity body to maximum density by the application of a continuous working force applied substantially throughout the operation of working to maximum density.

5. The method of forming a ferrous metal sheet comprising'commencing with a subdensity cohered metal body having an average grain size of less than one-fiftieth of an inch and of a width conforming to the width of said sheet, and a length conforming to the length of said sheet, having regard to elongation of said body in any direction no greater than that required to compact said body to a maximum density, heating said body to a temperature insufficient to melt said body but sufficient to avoid structural impairments thereof during working, and finally working said subdensity body to a maximum density by the application of a continuous Working force applied substantially throughout the operation of working to maximum density.

References Cited in the file of this patent UNITED STATES PATENTS 2,686,118 Cavanagh Aug. 10, 1954 

4. THE METHOD OF FORMING A METAL PRODUCT WHICH COMPRISES COMMENCING WITH A SUBDENSITY COHERED METAL BODY HAVING AN AVERAGE GRAIN SIZE OF LESS THAN ONE-FIFTIETH OF AN INCH AND IN WHICH THE WIDTH THEREOF IS GREATER THAN TEN TIMES THE THICKNESS, HEATING SAID BODY TO A TEMPERATURE INSUFFICIENT TO MELT SAID BODY BUT SUFFICIENT TO AVOID STRUCTURAL IMPAIRMENT THEREOF DURING WORKING, AND FINALLY WORKING SAID SUBDENSITY BODY TO MAXIMUM DENSITY BY THE APPLICATION OF A CONTINUOUS WORKING FORCE APPLIED SUBSTANTIALLY THROUGHOUT THE OPERATION OF WORKING TO MAXIMUM DENSITY. 